Optical assembly with coating and methods of use

ABSTRACT

Coated nanotubes and bundles of nanotubes are formed into membranes useful in optical assemblies in EUV photolithography systems. These optical assemblies are useful in methods for patterning materials on a semiconductor substrate. Such methods involve generating, in a UV lithography system, UV radiation. The UV radiation is passed through a coating layer of the optical assembly, e.g., a pellicle assembly. The UV radiation that has passed through the coating layer is passed through a matrix of individual nanotubes or matrix of nanotube bundles. UV radiation that passes through the matrix of individual nanotubes or matrix of nanotube bundles is reflected from a mask and received at a semiconductor substrate.

BACKGROUND

The present disclosure relates to the field of ultraviolet and extremeultraviolet lithography and to optical assemblies used in ultravioletand extreme ultraviolet lithography.

In the semiconductor integrated circuit (IC) industry, technologicaladvances in IC materials and design have produced generations of ICswhere each generation has smaller and more complex circuits than theprevious generation. In the course of IC evolution, functional density(i.e., the number of interconnected devices per chip area) has generallyincreased while geometry size (i.e., the smallest component (or line)that can be created using a fabrication process) has decreased. Thisscaling down process generally provides benefits by increasingproduction efficiency and lowering associated costs. Such scaling downhas also increased the complexity of IC processing and manufacturing.

A photolithography process forms a patterned resist layer for variouspatterning processes, such as etching or ion implantation. The minimumfeature size that may be patterned by way of such a lithography processis limited by the wavelength of the projected radiation source.Lithography machines have gone from using ultraviolet light with awavelength of 365 nanometers to using deep ultraviolet (DUV) lightincluding a krypton fluoride laser (KrF laser) of 248 nanometers and anargon fluoride laser (ArF laser) of 193 nanometers, and to using extremeultraviolet (EUV) light of a wavelength of 13.5 nanometers, improvingthe resolution at every step.

In the photolithography process, a photomask (or mask) is used. The maskincludes a substrate and a patterned layer that defines an integratedcircuit to be transferred to a semiconductor substrate during thephotolithography process. The mask is typically included with a pellicleassembly, collectively referred to as a mask system. The pellicleassembly includes a transparent thin membrane and a pellicle frame,where the membrane is mounted over the pellicle frame. The pellicleprotects the mask from fallen particles and keeps the particles out offocus so that they do not produce a patterned image, which may causedefects in the patterned semiconductor substrate when the mask is beingused. The membrane is typically stretched and mounted over the pellicleframe, and is attached to the pellicle frame by glue or other adhesives.An internal space may be formed by the mask, the membrane, and thepellicle frame.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a lithography system in accordance withsome embodiments of the present disclosure.

FIG. 2 is a schematic cross-sectional view of a mask for use inembodiments of the present disclosure.

FIGS. 3A-3C are a top view, a perspective view, and a cross-sectionalview along line A-A′, respectively, of a mask pellicle system inaccordance with some embodiments of the present disclosure.

FIGS. 4A-4D are schematic cross-sectional views of several pelliclemembranes in accordance with embodiments described herein.

FIG. 5A is a schematic perspective view of a nanotube including apartially removed covering layer in accordance with embodiments of thepresent disclosure.

FIG. 5B is an illustration of a covering layer on an external surfaceand on an internal surface of a nanotube in accordance with embodimentsof the present disclosure.

FIG. 5C is a schematic perspective view of a nanotube including apartially removed covering layer and an adhesion layer in accordancewith embodiments of the present disclosure.

FIG. 6A is a schematic view of a nanotube bundle in accordance withembodiments of the present disclosure.

FIG. 6B is a cross-sectional view of a nanotube bundle including acovering layer in accordance with embodiments of the present disclosure.

FIGS. 7A-7D are illustrations of uncoated nanotubes, nanotubes afterdeposition of a coating layer, an exploded view of coated nanotubes anda further exploded view of the carbon nanotubes respectively, inaccordance with embodiments of the present disclosure.

FIG. 8 is a flowchart illustrating a method according to an embodimentof the present disclosure.

FIG. 9 is a flowchart illustrating a method according to an embodimentof the present disclosure.

FIG. 10 is a schematic illustration of a system for applying aprotective layer or a coating layer to a nanotube in accordance anembodiment of the present disclosure.

FIG. 11 is a flowchart illustrating a method according to an embodimentof the present disclosure.

DETAILED DESCRIPTION

In the following description, thicknesses and materials may be describedfor various layers and structures within an integrated circuit die.Specific dimensions and materials are given by way of example forvarious embodiments. Those of skill in the art will recognize, in lightof the present disclosure, that other dimensions and materials can beused in many cases without departing from the scope of the presentdisclosure.

The following disclosure provides many different embodiments, orexamples, for implementing different features of the described subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present description. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

“Vertical direction” and “horizontal direction” are to be understood asindicating relative directions. Thus, the horizontal direction is to beunderstood as substantially perpendicular to the vertical direction andvice versa. Nevertheless, it is within the scope of the presentdisclosure that the described embodiments and aspects may be rotated inits entirety such that the dimension referred to as the verticaldirection is oriented horizontally and, at the same time, the dimensionreferred to as the horizontal direction is oriented vertically.

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various embodiments of thedisclosure. However, one skilled in the art will understand that thedisclosure may be practiced without these specific details. In otherinstances, well-known structures associated with electronic componentsand fabrication techniques have not been described in detail to avoidunnecessarily obscuring the descriptions of the embodiments of thepresent disclosure.

Unless the context requires otherwise, throughout the specification andclaims that follow, the word “comprise” and variations thereof, such as“comprises” and “comprising,” are to be construed in an open, inclusivesense, that is, as “including, but not limited to.”

The use of ordinals such as first, second and third does not necessarilyimply a ranked sense of order, but rather may only distinguish betweenmultiple instances of an act or structure.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. Thus, the appearances of the phrases “in one embodiment” or“in an embodiment” in various places throughout this specification arenot necessarily all referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be combined inany suitable manner in one or more embodiments.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contentclearly dictates otherwise. It should also be noted that the term “or”is generally employed in its sense including “and/or” unless the contentclearly dictates otherwise.

Embodiments in accordance with the present disclosure provide opticalassemblies suitable for transmitting UV or EUV radiation and protectingUV or EUV reflecting components of a lithography system. The opticalassemblies exhibit desirable UV/EUV transmission levels and promote heattransfer from the optical assembly. The optical assemblies are alsoresistant to damage from exposure to gases such as hydrogen, oxygen andH+ gas.

The various advantages and purposes of embodiments in accordance withthe present disclosure as described above and hereafter are achieved byproviding, according to aspects of the present disclosure an opticalassembly that includes the matrix of a plurality of nanotube bundles ora matrix of individual nanotubes. In accordance with some embodiments,the individual nanotubes are coated with a coating layer to protect thenanotubes. In other embodiments, the nanotube bundles are coated withthe coating layer; however, the individual nanotubes of the nanotubebundles are not individually coated with a coating layer. In otherembodiments the individual nanotubes of the nanotube bundles are coatedwith a coating layer and the nanotube bundle is formed from such coatedindividual nanotubes. These optical assemblies are useful in methods forpatterning materials on a semiconductor substrate. Such methods involvegenerating, in a UV lithography system, UV radiation. The UV radiationis passed through a coating layer of an optical assembly, e.g., apellicle assembly. The UV radiation that has passed through the coatinglayer is passed through a matrix of individual nanotubes or matrix ofnanotube bundles. UV radiation that passes through the matrix ofindividual nanotubes or matrix of nanotube bundles is reflected from amask and received at a semiconductor substrate. In accordance with otherembodiments, the coating layer is applied to a transparent layer of apellicle assembly.

Illustrated in FIG. 1 is a schematic view of a lithography system 100,in accordance with some embodiments. The lithography system 100 may alsobe generically referred to as a scanner that is operable to performlithographic processes including exposure with a respective radiationsource and in a particular exposure mode. In at least some of thepresent embodiments, the lithography system 100 includes an ultraviolet(UV) lithography system designed to expose a resist layer with UVradiation, i.e., UV light. Inasmuch, in various embodiments, the resistlayer includes a material sensitive to the UV light (e.g., a UV resist).The lithography system 100 of FIG. 1 includes a plurality of subsystemssuch as a radiation source 102, an illuminator 104, a mask stage 106configured to receive a mask 108, projection optics 110, and a substratestage 118 configured to receive a semiconductor substrate 116. Thefollowing description of a UV photolithography system in accordance withembodiments of the present disclosure refers to extreme ultravioletradiation as an example of ultraviolet radiation. Embodiments inaccordance with the present disclosure are not limited to extremeultraviolet radiation lithography systems. In other words, embodimentsdescribed with reference to extreme ultraviolet lithography systemsinclude embodiments that utilize ultraviolet radiation. A generaldescription of the operation of the lithography system 100 is asfollows: EUV light from the radiation source 102 is directed toward theilluminator 104 (which includes a set of reflective mirrors) andprojected is onto the reflective mask 108. A reflected mask image isdirected toward the projection optics 110, which focuses the EUV lightand projects the EUV light onto the semiconductor substrate 116 toexpose a EUV resist layer deposited thereupon. Additionally, in variousexamples, each subsystem of the lithography system 100 may be housed in,and thus operate within, a high-vacuum environment, for example, toreduce atmospheric absorption of the EUV light.

In the embodiments described herein, the radiation source 102 may beused to generate the EUV light. In some embodiments, the radiationsource 102 includes a plasma source, such as for example, a dischargeproduced plasma (DPP) or a laser produced plasma (LPP). In someexamples, the EUV light may include light having a wavelength rangingfrom about 1 nm to about 100 nm. In one particular example, theradiation source 102 generates EUV light with a wavelength centered atabout 13.5 nm. Accordingly, the radiation source 102 may also bereferred to as a EUV radiation source 102. In some embodiments, theradiation source 102 also includes a collector, which may be used tocollect EUV light generated from the plasma source and to direct thecollected EUV light toward imaging optics such as the illuminator 104.

As described above, EUV light from the radiation source 102 is directedtoward the illuminator 104. In some embodiments, the illuminator 104 mayinclude reflective optics (e.g., for the EUV lithography system 100),such as a single mirror or a mirror system having multiple mirrors inorder to direct light from the radiation source 102 onto the mask stage106, and particularly to the mask 108 secured on the mask stage 106. Insome examples, the illuminator 104 may include a zone plate (not shown),for example, to improve focus of the EUV light. In some embodiments, theilluminator 104 may be configured to shape the EUV light passing therethrough in accordance with a particular pupil shape, and including forexample, a dipole shape, a quadrapole shape, an annular shape, a singlebeam shape, a multiple beam shape, and/or a combination thereof. In someembodiments, the illuminator 104 is operable to configure the mirrors(i.e., of the illuminator 104) to provide a desired illumination to themask 108. In one example, the mirrors of the illuminator 104 areconfigurable to reflect EUV light to different illumination positions.In some embodiments, a stage (not shown) prior to the illuminator 104may additionally include other configurable mirrors that may be used todirect the EUV light to different illumination positions within themirrors of the illuminator 104. In some embodiments, the illuminator 104is configured to provide an on-axis illumination (ONI) to the mask 108.In some embodiments, the illuminator 104 is configured to provide anoff-axis illumination (OAI) to the mask 108. It should be noted that theoptics employed in the EUV lithography system 100, and in particularoptics used for the illuminator 104 and the projection optics 110, mayinclude mirrors having multilayer thin-film coatings known as Braggreflectors. By way of example, such a multilayer thin-film coating mayinclude alternating layers of Mo and Si, which provides for highreflectivity at EUV wavelengths (e.g., about 13 nm).

As discussed above, the lithography system 100 also includes the maskstage 106 configured to secure the mask 108 within the lithographysystem. Since the lithography system 100 may be housed in, and thusoperate within, a high-vacuum environment, the mask stage 106 mayinclude an electrostatic chuck (e-chuck) to secure the mask 108. As withthe optics of the EUV lithography system 100, the mask 108 is alsoreflective. Details of the mask 108 are discussed in more detail belowwith reference to the example of FIG. 2. As illustrated in FIG. 1, lightis reflected from the mask 108 and directed towards the projectionoptics 110, which collects the EUV light reflected from the mask 108. Byway of example, the EUV light collected by the projection optics 110(reflected from the mask 108) carries an image of the pattern defined bythe mask 108. In various embodiments, the projection optics 110 providesfor imaging the pattern of the mask 108 onto the semiconductor substrate116 secured on the substrate stage 118 of the lithography system 100. Inparticular, in various embodiments, the projection optics 110 focusesthe collected EUV light and projects the EUV light onto thesemiconductor substrate 116 to expose a EUV resist layer deposited onthe semiconductor substrate 116. As described above, the projectionoptics 110 may include reflective optics, as used in EUV lithographysystems such as the lithography system 100. In some embodiments, theilluminator 104 and the projection optics 110 are collectively referredto as an optical module of the lithography system 100.

As discussed above, the lithography system 100 also includes thesubstrate stage 118 to secure the semiconductor substrate 116 to bepatterned. In various embodiments, the semiconductor substrate 116includes a semiconductor wafer, such as a silicon wafer, germaniumwafer, silicon-germanium wafer, III-V wafer, or other type of wafer. Thesemiconductor substrate 116 may be coated with a resist layer (e.g., anEUV resist layer) sensitive to EUV light. EUV resists may have stringentperformance standards. For purposes of illustration, an EUV resist maybe designed to provide at least around 22 nm resolution, at least around2 nm line-width roughness (LWR), and with a sensitivity of at leastaround 15 mJ/cm2. In the embodiments described herein, the varioussubsystems of the lithography system 100, including those describedabove, are integrated and are operable to perform lithography exposingprocesses including EUV lithography processes. To be sure, thelithography system 100 may further include other modules or subsystemswhich may be integrated with (or be coupled to) one or more of thesubsystems or components described herein.

The lithography system may include other components and may have otheralternatives. In some embodiments, the lithography system 100 mayinclude a pupil phase modulator 112 to modulate an optical phase of theEUV light directed from the mask 108, such that the light has a phasedistribution along a projection pupil plane 114. In some embodiments,the pupil phase modulator 112 includes a mechanism to tune thereflective mirrors of the projection optics 110 for phase modulation.For example, in some embodiments, the mirrors of the projection optics110 are configurable to reflect the EUV light through the pupil phasemodulator 112, thereby modulating the phase of the light through theprojection optics 110. In some embodiments, the pupil phase modulator112 utilizes a pupil filter placed on the projection pupil plane 114. Byway of example, the pupil filter may be employed to filter out specificspatial frequency components of the EUV light reflected from the mask108. In some embodiments, the pupil filter may serve as a phase pupilfilter that modulates the phase distribution of the light directedthrough the projection optics 110.

Referring to FIG. 2, the mask 108 includes a patterned image comprisingone or more absorbers 208 having an anti-reflective coating (ARC) layer210. The one or more absorbers 208 and anti-reflective coating are on amulti-layer structure 204, e.g., Mo—Si multi-layers, which is on asubstrate 202. Examples of the materials for the absorbers 208 include atantalum nitride layer or a Ta_(x)B_(y)O_(z)N_(u). Examples of materialsfor the antireflective coating layer include Ta_(x)B_(y)O_(z)N_(u), anHf_(x)O_(y) layer or a Si_(x)O_(y)N_(z) layer. An example of a substrate202 includes a low thermal expansion material substrate, such as TiO₂doped SiO₂. In the illustrated embodiment of FIG. 2, the multi-layerstructure 204 is covered by a capping layer 206 and the backside ofsubstrate 202 is covered with a backside coating layer 203. An exampleof a material for capping layer 206 includes ruthenium. An example of amaterial for backside coating layer 203 includes chromium nitride.

As discussed above, the mask 108 is used to transfer circuit and/ordevice patterns onto a semiconductor wafer (e.g., the semiconductorsubstrate 116) by the lithography system 100. To achieve a high fidelitypattern transfer from the patterned mask 108 to the semiconductorsubstrate 116, the lithography process should be defect free. Unwantedparticles, e.g., particles of Sn that are used to generate the EUV lightin the radiation source 102 may be unintentionally deposited on thesurface of the capping layer 206 and can result in degradation oflithographically transferred patterns if not removed. Particles may beintroduced by any of a variety of methods besides as part of the EUVlight generation, such as during an etching process, a cleaning process,and/or during handling of the EUV mask 108. Accordingly, the mask 108 isintegrated with a pellicle and is protected by the pellicle assembly.The mask and the pellicle assembly are collectively referred to as amask-pellicle system. For example, during the lithography patterningprocess by the lithography system 100, the mask-pellicle system issecured to the mask stage 106.

With reference to FIGS. 3A, 3B, and 3C, illustrated therein is atop-view, a perspective view, and a cross-sectional view along lineA-A′, respectively, of a mask pellicle system 300. Referring to FIGS.3A, 3B, and 3C, the mask pellicle system 300 and a method of using thesame are described. While embodiments of the present disclosure aredescribed with reference to a mask of a photolithography system, it isunderstood that the embodiments of the present disclosure are usefulwith other UV or EUV reflecting components of a lithography system thatreflect UV or EUV radiation.

The mask pellicle system 300 includes a mask 302, a pellicle frame 304and an optical assembly, e.g., membrane (or pellicle membrane) 306integrated together through adhesive material layers 308 and 310. Asdiscussed above, the mask 302 also includes a patterned surface 314 usedto pattern a semiconductor substrate by a lithographic process. In someembodiments, the mask 302 may be substantially the same as the mask 108,discussed above. In the present embodiment, the mask 302 is integratedin the mask pellicle system 300 and is secured on the mask stage 106collectively with the membrane 306 and the pellicle frame 304 during alithography patterning process.

The membrane 306 is configured proximate to the mask 302 and is attachedto the pellicle frame 304 through the adhesive layer 308. Particularly,the membrane 306 is attached to the pellicle frame 304 through theadhesive material layer 308. The mask 302 is further attached to thepellicle frame 304 through the adhesive material layer 310. Thus, themask 302, the pellicle frame 304 and the membrane 306 are thusconfigured and integrated to enclose an internal space 312. Thepatterned surface 314 of the mask 302 is enclosed in the internal space312 and is therefore protected from contamination during a lithographypatterning process, mask shipping, and mask handling. In the illustratedembodiment of FIG. 3C, pellicle frame 304 is provided with two ventholes 320. Embodiments in accordance with the present disclosure caninclude only a single vent hole 320 or include more than two vent holes320. Vent holes serve to equalize air pressure between the open spacebounded by the pellicle frame 304 and the pellicle membrane 306 and theenvironment outside the pellicle frame 304 and pellicle membrane 306.Vent holes 320 can be provided with filters (not shown) configured toprevent particles from entering vent holes 320.

The membrane 306 is made of a thin film transparent to the radiationbeam used in a lithography patterning process, and furthermore has athermal conductive surface. The membrane 306 is also configuredproximate to the patterned surface 314 on the mask 302 as illustrated inFIG. 3C. In various embodiments, the membrane 306 includes a transparentmaterial layer with a thermal conductive film on one surface (or bothsurfaces).

FIG. 4 is a cross-sectional view of the membrane 306, constructed inaccordance with some embodiments. The membrane 306 includes atransparent layer 402 or core material layer of one or more materialsincluding silicon, such as polycrystalline silicon (poly-Si), amorphoussilicon (a-Si), doped silicon (such as phosphorous doped silicon SiP orSiC) or a silicon-based compound, such as SiN or MoSi_(x)N_(y) orcombination (SiN/MoSiN). Alternatively, the transparent layer 402includes polymer, graphene, carbon network membrane, carbon nanotubes,silicon carbon nanotube, boron nitride nanotube, carbon nanotube bundlesor other suitable material, including bundles of nanotubes. In someembodiments, the membrane 306 is characterized by the absence of oxygencontaining materials, e.g., SiO₂. Membranes 306 without oxygencontaining materials are less susceptible to degradation caused by H⁺radicals that membranes 306 are exposed to during the photolithographyprocess or during maintenance of the photolithography system. When amembrane 306 containing oxygen containing materials, such as SiO₂ isexposed to H+ radicals, peeling of coatings provided on the SiO₂ hasbeen observed. The transparent layer 402 has a thickness with enoughmechanical strength, but in some embodiments, not a thickness thatdegrades the transparency of the membrane to extreme ultravioletradiation from the radiation source by more than 15% in someembodiments, more than 10% in some embodiments or more than 5% in someembodiments. In some examples, the transparent layer 402 has a thicknessranging between 30 nm and 50 nm.

In some embodiments, the membrane 306 includes a first coating layer 404formed on the external surface 322 of the transparent layer 402 and asecond coating layer 406 formed on the internal surface 324 of thetransparent layer 402. In FIG. 4A, the external surface 322 of thetransparent layer 402 is its top surface and the internal surface 324 ofthe transparent layer 402 is its bottom surface. In accordance with theembodiment illustrated in FIG. 4A, the material of the coating layer 404is the same as the material of the coating layer 406. In otherembodiments in accordance with FIG. 4A, the material of the coatinglayer 404 is different from the material of the coating layer 406. Inyet other embodiments in accordance with FIG. 4A, coating layer 404comprises multiple layers of material. Similarly, in other embodiments,coating layer 406 comprises multiple layers of material. Such multiplelayers can include the same material or different materials. Inaddition, the multiple layers of material making up coating layer 404and/or coating layer 406 can be the same thickness or can be differentthicknesses. In FIG. 4B, the coating layer 406 is provided only on theinternal surface 324 and not the external surface 322. In otherembodiments in accordance with FIG. 4B, coating layer 406 comprisesmultiple layers of material. In addition, the multiple layers ofmaterial making up coating layer 406 in FIG. 4B can be the samethickness or can be different thicknesses. In FIG. 4C, the coating layer404 is provided only on the external surface 322 and not the internalsurface 324. In other embodiments in accordance with FIG. 4C, coatinglayer 404 comprises multiple layers of material. In addition, themultiple layers of material making up coating layer 404 in FIG. 4B canbe the same thickness or can be different thicknesses. The coating layer(404 or 406) protects the transparent layer 402 from attack, such as bychemicals and/or particles. In some embodiments, the coating layer 404and 406 promotes heat transfer from the transparent layer 402. Inaccordance with another embodiment of the present disclosure, FIG. 4Dillustrates an example where a first coating layer 408 a is ontransparent layer 402 and a second coating layer 408 b is on firstcoating layer 408 a. In accordance with the embodiment of FIG. 4D, thematerial of the first coating layer 408 a and the material of the secondcoating layer 408 b may be the same or they may be different. (forexample: 408 a: MoSiN and 408 b:SiN2)

In accordance with some embodiments of the present disclosure, choice ofa particular material for use as first coating layer 404 and/or secondcoating layer 406 should take into consideration a number of differentfactors, including how thick a layer of material is needed to provide aconformal coating, the scattering effect of the material on UV or EUV,transmission of the UV or EUV and reflection of the UV or EUV,absorption of the UV or EUV, resistance to desorption of oxygen andattack by ionized gases that come in contact with the coating layers,e.g., H+ gas.

For example, materials which are susceptible to being applied as athinner coat while providing a conformal coating are preferred overmaterials that require application of a thicker coat to provide aconformal coating. In some embodiments, coating layers 404 or 406 have athickness on the order of 1 to 10 nanometers.

Materials which scatter less of the EUV radiation directed at the maskare preferred over materials that scatter more of the same EUVradiation. Examples of such materials include boron nitride (BN) andsilicon nitride (Si3N4). Ruthenium is not a suitable material forcoating layers in accordance with embodiments of the present disclosurebecause ruthenium exhibits a differential scattering cross-section ofEUV radiation at zero degrees and 360 degrees that is about 6 timesgreater than the differential scattering cross-section of EUV radiationat zero degrees and 360 degrees for a transparent material coated withboron nitride or silicon nitride. Generally, a material with a lowerindex of refraction produces more scattering compared to a material witha higher index of refraction. Thus, when selecting a material forcoating layers 404 and 406 based only on its index of refraction, amaterial having a higher index of refraction would be preferred over amaterial having a lower index of refraction.

Generally, a material with a higher extinction coefficient k, indicatinga higher absorption of radiation, is less desirable than a materialexhibiting a lower extinction coefficient k because the material with ahigher extinction coefficient will transmit less UV or EUV. Thus, whenselecting a material for coating layers 404 and 406 based only on itsextinction coefficient k, a material having a lower extinctioncoefficient would be preferred over a material having a higherextinction coefficient.

Materials which transmit more of the UV or EUV radiation directed at themask are preferred over materials that transmit less of the same UV orEUV radiation. For example, in some embodiments, materials that transmit80% or more of the radiation directed at the mask are suitable. In otherembodiments, materials that transmit 85% or more of the radiationdirected at the mask are suitable. In yet other embodiments, materialsthat transmit 90% or more of the radiation directed at the mask aresuitable. In other embodiments, materials that transmit 95% or more ofthe radiation directed at the mask are suitable.

Materials that reflect less of the radiation to be directed at the maskare preferred over materials that reflect more of the same EUVradiation.

Materials that absorb less of the EUV radiation to be directed at themask are preferred over materials that absorb more of the same EUVradiation.

Materials that are more resistant to desorption of oxygen are preferredover materials that are less resistant to desorption of oxygen.

Materials that include higher valence oxides are less suitable asmaterials for coating layer 404 or 406 because they are susceptible toradiation stimulated desorption of oxygen initiated by creation of holesin shallow core levels. These resulting holes cause the coating layer tobe more reactive with gas molecules the coating layer is exposed toduring the photolithography process or maintenance processes as comparedto the reactivity of a coating layer that does not include highervalence oxides. In accordance with embodiments of the presentdisclosure, materials that do not include higher valence oxides arepreferred over materials that include higher valence oxides.

Particles, e.g., Sn particles, from the source of EUV radiation may fallon the pellicle surface. Removal of such particles is achieved byetching the pellicle surface with an ionized gas, such as H+. Theability of the ionized gas to etch the particles, e.g., Sn particles,from the pellicle surface depends in part on the difference inelectronegativity between Sn and the material of the pellicle surface.Accordingly, selection of a material suitable for coating layers 404and/or 406 takes into consideration the difference in theelectronegativity between the particle to be etched, e.g., Sn particlehaving an electronegativity of 1.96, and the material of the coatinglayer. Materials having an electronegativity less than theelectronegativity of the particle to be etched are preferred as thematerial for the coating layers compared to materials having anelectronegativity greater than the electronegativity of the particle tobe etched from the coating layer surface. In accordance with someembodiments, material suitable for coating layers 404 and/or 406 includematerials having an electronegativity less than 1.96 down to about −0.2.

Examples of materials useful for coating layers 404 and/or 406 takinginto consideration the criteria described above are presented below.

In some embodiments, the coating layer 404 includes boron (B), boronnitride (BN), boron silicon nitride (BNSi), boron carbide (B4C), boronsilicon carbide (BCSi), silicon mononitride (SiN), silicon nitride(Si3N4), silicon dinitride (SiN2), silicon carbide (SiC), silicon carbonnitride (SiCxNy), niobium (Nb), niobium nitride (NbN), niobiummonosilicide (NbSi), niobium silicide (NbSi2), niobium silicon nitride(NbSiN), niobium titanium nitride (NbTixNy), zironcium nitride (ZrN),zirconium fluoride (ZrF4), yttrium nitride (YN), yttrium fluoride (YF),molybdenum (Mo), molybdenum nitride (MoN2), molybdenum carbide (Mo4C andMo2C), molybdenum silicide (MoSi2), molybdenum silicon nitride(MoSixNy), ruthenium-niobium alloys (RuNb), ruthenium silicon nitride(RuSiN), titanium nitride (TiN), titanium carbon nitride (TiCxNy),hafnium nitride (HfNx), hafnium fluoride (HfF4) or vanadium nitride(VN). Materials for coating layer 404 exclude materials that includehigher valence oxides, such as TiO₂, V₂O₅, ZrO₂, Ta₂O₅, MoO₃, WO₃, CeO₂,Er₂O₃, SiO₂, Y₂O₃, Nb₂O₅, V₂O₃ and HfO₂.

In some embodiments, materials for coating layer 404 are selected frommaterials that do not include higher valence oxides, such as boron (B),boron silicon nitride (BNSi), silicon nitride (Si3N4), silicon dinitride(SiN2), niobium (Nb), niobium nitride (NbN), niobium monosilicide(NbSi), niobium silicide (NbSi2), niobium silicon nitride (NbSiN),niobium titanium nitride (NbTixNy), zironcium nitride (ZrN), zirconiumfluoride (ZrF4), yttrium nitride (YN), yttrium fluoride (YF), molybdenum(Mo), molybdenum nitride (MoN2), molybdenum silicide (MoSi2), molybdenumsilicon nitride (MoSixNy), ruthenium-niobium alloys (RuNb), rutheniumsilicon nitride (RuSiN), titanium nitride (TiN), titanium carbon nitride(TiCxNy), hafnium nitride (HfNx), hafnium fluoride (HfF4) or vanadiumnitride (VN).

In some embodiments, materials for coating layer 404 are selected frommaterials that do not include ruthenium or molybdenum, such as boron(B), boron silicon nitride (BNSi), silicon nitride (Si3N4), silicondinitride (SiN2), niobium (Nb), niobium nitride (NbN), niobiummonosilicide (NbSi), niobium silicide (NbSi2), niobium silicon nitride(NbSiN), niobium titanium nitride (NbTixNy), zironcium nitride (ZrN),zirconium fluoride (ZrF4), yttrium nitride (YN), yttrium fluoride (YF),titanium nitride (TiN), titanium carbon nitride (TiCxNy), hafniumnitride (HfNx), hafnium fluoride (HfF4) or vanadium nitride (VN).

In some embodiments, the coating layer 404 includes boron siliconnitride (BNSi), boron silicon carbide (BCSi), molybdenum carbide (Mo4C)or molybdenum carbide (Mo2C).

The coating layer 404 is thin and does not degrade the transparency ofthe membrane 306 to UV or EUV light. In some examples, the thickness ofthe coating layer (404 and 406 as well if it is present) ranges between1 nm and 10 nm. One example of a coating layer has a thickness of 5 nmwith a variation of 10% or less. The coating layer may be formed by asuitable deposition technique, such as chemical vapor deposition (CVD),atomic layer deposition (ALD), plasma enhanced ALD (PEALD), physicalvapor deposition (PVD), e-beam deposition, electrodeposition,electroless deposition or other suitable technique.

In accordance with some embodiments of the present disclosure, thecoating layer 404 also serves as a thermal conductive layer whichpromotes the transfer of thermal energy from transparent layer 402 tothe environment around the coating layer 404.

In accordance with some embodiments of the present disclosure, thetransparent layer 402, (core membrane) is treated prior to applicationof the coating layer 404 or coating layer 406 to produce minor defectsin the surface of transparent layer 402 and/or to remove unwantedsilicon dioxide. Producing minor defects in the surface of transparentlayer 402 and/or removing unwanted silicon dioxide improves the adhesionof coating layer 404 or coating layer 406 to the surface of transparentlayer 402. Examples of suitable processes to treat the surface oftransparent layer 402 prior to application of coating layers 404 or 406include nitrogen, oxygen, carbon fluoride or argon gas plasma treatment.The transparent layer 402 is treated with the gas plasma using acombination of frequency, power, pressure and period of time sufficientto create minor defects in the surface of the transparent layer 402which will improve adhesion of the coating layer and/or to removeunwanted silicon dioxide.

The mask pellicle system 300 also includes a pellicle frame 304configured such that the membrane 306 can be attached and secured to thepellicle frame 304. The pellicle frame 304 may be designed in variousdimensions, shapes, and configurations. Among those and otheralternatives, the pellicle frame 304 may have one single component ormultiple components. The pellicle frame 304 includes a material withmechanical strength, and designed in a shape, dimensions, and aconfiguration so as to secure the membrane 306 properly across thepellicle frame 304. In some embodiments, the pellicle frame 304 may beentirely formed by a porous material.

The pellicle frame 304 includes a porous material designed forventilation and pressure balance since the pellicle-mask system 300 isin a vacuum environment when secured on the mask stage 106 during thelithography patterning process. As illustrated in FIG. 3C, the porousmaterial of the pellicle frame 304 has connected-pore channels extendingfrom an internal surface 316 to an external surface 318 of the pellicleframe 304 for ventilation. Alternatively as discussed above, pellicleframe 304 includes one or more vents 320 for ventilation and pressurebalancing.

In accordance with another embodiment of the present disclosure, atransparent layer comprises a plurality of nanotubes forming a matrix ofnanotubes, e.g., carbon nanotubes, boron-nitride nanotubes, siliconcarbide nanotubes or combinations thereof. In some embodiments, thetransparent layer including the nanotubes is porous. Techniques forforming sheets of a plurality of nanotubes are known. Such sheets ofnanotubes when treated in accordance with embodiments of the presentdisclosure form a combination of a transparent layer and a coating layerthat are useful in optical assemblies, e.g., a pellicle membrane, inaccordance with embodiments of the present disclosure.

In accordance with embodiments of the present disclosure, the carbonnanotubes are single wall nanotubes or multi-walled nanotubes. In someembodiments, the nanotubes are carbon nanotubes. The nanotubes may beoriented nanotubes or they may be non-oriented nanotubes. The nanotubesmay be individual, unbundled nanotubes or the nanotubes maybe be bundledindividual nanotubes. Carbon nanotubes are susceptible to degradationfrom exposure to hydrogen gas or oxygen gas, such as the type employedduring operation or maintenance of a photolithography system.

Referring to FIG. 5A, an embodiment of the present disclosure includesan unbundled single wall carbon nanotube 500 including a coating layer502 formed on outer surface 504 from one or more of the materialsdescribed above for coating layers 404 and/or 406. As with priordescribed embodiments, coating layer 502 can comprise a single layer ofthe same material or can comprise multiple layers of the same materialor multiple layers of different materials. Coating layer 502 has athickness t. In some embodiments, t is 1 to 10 nanometers. FIG. 5B is anillustration of a cross-section of a coated carbon nanotube inaccordance with embodiments of the present disclosure. FIG. 5Billustrates how in accordance with some embodiments of the presentdisclosure, both the external surface 504 of carbon nanotube 500 and theinternal surface 506 of carbon nanotube 500 are coated with coatingmaterial 502.

In accordance with some embodiments of the present disclosure, thesurfaces of carbon nanotube 500 are treated prior to application of thematerial of coating layer 502 on outside surface 504 and inside surface506 to modify, i.e., produce minor defects in, the surface of carbonnanotube 500 and/or to introduce functional groups, e.g., hydrophilicgroups, to the surfaces of the carbon nanotube. Modifying the surfacesof carbon nanotube 500 improves the adhesion of coating layer 502 on theouter surface 504 or the inner surface 506 of carbon nanotube 500.Examples of suitable processes to treat the surfaces of carbon nanotube500 prior to application of coating layer 502 include nitrogen, oxygen,carbon fluoride or argon gas plasma treatment. In accordance with someembodiments, the surfaces of the carbon nanotube 500 are treated withthe gas plasma using a combination of frequency, power, pressure andperiod of time sufficient to achieve the desired surface modificationsto improve adhesion of coating layer 502 to the nanotube surfaces. Inaccordance with one embodiment, the carbon nanotube is treated withoxygen plasma at a frequency of about 13.6 MHz at a power of about100-200 W and a pressure of about 1-200 mTorr. The length of time thatthe carbon nanotube is so treated is sufficient to provide the desiredsurface modifications without damaging the carbon nanotubes.

Referring to FIG. 5C, in other embodiments, the surfaces of thenanotubes 500, e.g., carbon nanotubes, are coated with a layer 508 whichpromotes adhesion between the surface of the carbon nanotube 500 and thecoating layer 502. Such adhesion promoting materials are coated ontosurfaces of the carbon nanotubes 500 by deposition processes such as ALDand PEALD. Examples of materials of layer 508 include amorphous carbonor other materials which can be deposited by ALD or PEALD processes andpromote adhesion between the surfaces of the carbon nanotubes 500 andthe coating layer 502. In accordance with another embodiment of thepresent disclosure, layer 508 is a protective layer that serves toprotect the nanotubes from degradation by a plasma of a PEALD processused to deposit the coating layer 502. When a protective layer is formedon the nanotubes, it is formed by a first deposition process, forexample, a thermal atomic layer deposition process in the absence of anyplasma. Multiple cycles of the first deposition process can be employedin order to form multiple protective layers on the nanotubes. After oneor more protective layers has been formed on the nanotubes, the coatinglayer 502 can be deposited using a second deposition process, forexample, plasma enhanced atomic layer deposition (PEALD) techniques. Dueto the presence of the protective layer, the nanotubes of the membraneare not damaged by the plasma of the PEALD process. Examples ofmaterials useful as a protective layer include the same materialsdescribed above for forming coating layer 502.

Referring to FIG. 6A, another embodiment of the utilization of nanotubesin an optical assembly, e.g., a pellicle membrane 306, includes bundlingmultiple nanotubes. In FIG. 6A, seven nanotubes 600 a-600 g are bundledto form a nanotube bundle 602. Techniques for bundling nanotubes to forma nanotube bundle 602 useful in embodiments in accordance with thepresent disclosure are known. In other embodiments, the number ofnanotubes making up nanotube bundle 602 is less than seven or is greaterthan seven. Reducing the number of individual carbon nanotubes formingthe nanotube bundle 602 reduces the index of refraction of the nanotubebundle 602. As noted above, reducing the index of refraction has theeffect of reducing the scattering of incident EUV radiation, which hasthe effect of increasing the transmission of incident EUV radiation.Thus, in some embodiments, a nanotube bundle including fewer individualnanotubes would be preferred over a nanotube bundle including a largernumber of individual nanotubes.

Referring to FIG. 6B, in accordance with embodiments of the presentdisclosure, the nanotube bundle 602 is coated with or surrounded by acoating layer 604. The description of materials useful for coatinglayers 404 and 406 above is applicable to the materials used for coatinglayer 604. In the embodiment illustrated in FIG. 6B, the coating layer604 is shown as surrounding the nanotube bundle 602 but is not coveringall of the surfaces of the individual nanotubes 600 a-600 g. Inaccordance with other embodiments, coating layer 604 coats more of thesurfaces of the individual nanotubes 600 a-600 b than is depicted inFIG. 6B. For example, coating layer 604 can coat the surfaces ofnanotubes 600 a-600 e and 600 g that are exposed on the exterior of thenanotube bundle 602. In such embodiment, the outer surface of nanotube600 f is not coated with coating layer 604. In other embodiments, theouter surface of each of the seven nanotubes 600 a-600 g are coated withthe material making up coating layer 604. In other embodiments thetransparent layer includes individual nanotubes that have been partiallyor completely coated with coating layer 604, bundled to form nanotubebundle 602 and then the nanotube bundle is coated/surrounded with anadditional layer of coating material 604. In some embodiments, thecoating layer 604 covers the entire surface of the nanotube upon whichit resides; however, in other embodiments, the coating layer covers lessthan the entire surface of the nanotube upon which it resides.

In the embodiment of FIGS. 6A and 6B, the individual nanotubes are shownas being closely and tightly packed together. In other embodiments, theindividual nanotubes may not be packed as closely and tightly asillustrated in FIGS. 6A and 6B. For example, in other embodiments,portions of the outer surfaces of the nanotubes may not be in contactwith each other.

In another embodiment, pellicle membrane 306 includes a plurality ofnanotube bundles 602 and a plurality of individual unbundled nanotubes500. In this embodiment, the plurality of nanotube bundles 602 and theplurality of individual unbundled nanotubes 500 are coated in accordancewith the description above.

The description above regarding the selection of a particular materialfor coating layer 404 applies equally to the selection of a particularmaterial for coating layer 604. The description above regarding thelayer 508 as an adhesion layer or a protective layer applies equally tothe use of layer 508 in combination with the nanotube bundles of FIGS.6A and 6B and the coating layer 604.

Nanotube embodiments in accordance with FIGS. 5A, 5B, 6A and 6B providea pellicle membrane 306 that transmits 85% or more of UV or EUVradiation incident on the transparent layer. In other embodiments,pellicle membrane 306 comprising coated nanotubes or coated nanotubebundles transmits 90% or more of UV or EUV radiation incident on thetransparent layer. In some embodiments, pellicle membrane 306 comprisingcoated nanotubes or coated nanotube bundles transmits 95% or more of UVor EUV radiation incident on the transparent layer.

FIG. 7A is an image of a surface of a matrix of nanotubes beforedeposition of a coating layer. FIG. 7B is an image of the matrix ofnanotubes of FIG. 7A after a coating layer has been applied. FIG. 7C isan enlarged view of a portion of FIG. 7B. FIG. 7D is an enlarged view ofa portion of FIG. 7B.

Referring to FIG. 8, a method 800 in accordance with embodiments of thepresent disclosure for patterning a material on a semiconductorsubstrate in an EUV photolithography system is illustrated and describedwith reference to FIGS. 1 and 4A-4D. The method includes generating EUVradiation in step 820. EUV radiation can be generated, for example,utilizing the radiation source 102 of FIG. 1 as described above. Thegenerated EUV radiation is passed through a coating layer of a pelliclemembrane in step 830. Examples of a coating layer includes coatinglayers 404, 406, 502 or 604. Passing the generated EUV radiation thoughthe coating layer is accomplished in accordance with the descriptionabove for doing the same. An example of a pellicle membrane is pelliclemembrane 306. At step 840, the EUV radiation is passed through atransparent layer of the pellicle membrane. Examples of a transparentlayer of the pellicle membrane include the transparent layer 402described above with reference to FIGS. 4A-4C. Passing EUV radiationthrough a transparent layer of a pellicle membrane can be carried out inaccordance with the description above. EUV radiation that is passedthrough the transparent layer of the pellicle membrane is reflected froma mask at step 850. An example of a mask suitable for reflecting the EUVradiation is mask 108 described above. Mask 108 reflects EUV radiationas described above. At step 860, EUV radiation is received at asemiconductor substrate. An example of a semiconductor substrate issemiconductor substrate 116 described above.

Referring to FIG. 9, a method 900 in accordance with embodiments of thepresent disclosure for patterning a material on a semiconductorsubstrate in an EUV photolithography system is illustrated and describedbelow with reference to FIGS. 1 and 4A-4D. The method includesgenerating EUV radiation in step 920. EUV radiation can be generated,for example, utilizing the radiation source 102 of FIG. 1 as describedabove. The generated EUV radiation is passed through a coating layer ofa pellicle membrane in step 930. Examples of a coating layer includecoating layers 404, 406, 502 or 604. Passing the generated EUV radiationthough the coating layer is accomplished in accordance with thedescription above for doing the same. An example of a pellicle membraneis pellicle membrane 306. At step 940, the EUV radiation is passedthrough matrix of nanotubes of the pellicle membrane. Examples ofnanotubes of the pellicle membrane include the nanotubes and nanotubebundles described above with reference to FIGS. 5A, 5B, 6A and 6B.Passing EUV radiation through a matrix of nanotubes of a pelliclemembrane can be carried out in accordance with the description above.EUV radiation that is passed through the matrix of nanotubes of thepellicle membrane is reflected from a mask at step 950. An example of amask suitable for reflecting the EUV radiation is mask 108 describedabove. Mask 108 reflects EUV radiation as described above. At step 960,EUV radiation is received at a semiconductor substrate. An example of asemiconductor substrate is semiconductor substrate 116 described above.

FIG. 11 is a flowchart illustrating a method in accordance with thepresent disclosure for forming a protective, adhesion or coating layerson transparent layer 402 or a matrix of nanotubes formed into a membrane950. In method 1000 of FIG. 11, the transparent layer 402 or a matrix ofnanotubes provided as a membrane 950, e.g., on a frame or border 952 issupported, e.g., vertically, in a chamber 954 capable of carrying out athermal ALD or CVD process and a plasma-enhanced ALD or CVD process. Thetransparent layer 402 or the frame 952 is supported within chamber 942such that they have multiple freedoms of movement. For example in theembodiment illustrated in FIG. 10, frame 950 can be rotated around avertical axis or it can be tilted around the horizontal axis.Embodiments in accordance with the present disclosure are not limited torotating the frame around the vertical access or tilting it around thehorizontal axis. In other embodiments, the frame has freedom of movementin addition to rotation around a vertical axis or tilting around thehorizontal axis. Such rotation and tilting can be implemented during athermal process and/or a plasma-enhanced process to promotes evencoating of nanotubes of the membrane 950 with a coating layer, adhesionlayer or protective layer. Conditions within the chamber are maintainedto promote uniform deposition of the coating layer, adhesion layer orprotective layer, e.g., temperatures in the range of 500 degrees Celsiusto 1200 degrees Celsius. Such temperatures are provided by providingthermal energy from the chamber walls or heaters associated with thechamber walls. Embodiments in accordance with the present disclosure forforming protective, adhesion or coating layers on a matrix of nanotubesor transparent layer 402 are not limited to utilizing thermal PVD or CVDand plasma enhanced PVD or CVD. For example, such layers can be formedusing ion beam deposition techniques. The description above regardingutilizing thermal PVD or CVD and plasma enhanced PVD or CVD also appliesto the use of ion beam deposition. At step 1030, a protective layer isformed on the transparent layer or nanotubes of the membrane by athermal atomic layer deposition process. The chamber 942 illustrated inFIG. 10 is an example of a chamber where both thermal atomic layerdeposition and plasma enhanced atomic layer deposition can be carriedout. Method 1000 is not limited to utilizing a single chamber in whichboth thermal and plasma enhanced atomic layer deposition is carried out.For example, in other embodiments, the thermal deposition process can becarried out in one chamber and the plasma enhanced deposition can becarried out in another different chamber.

In one embodiment, the present disclosure describes an optical assembly,e.g., a pellicle assembly, including a matrix of a plurality of nanotubebundles. In such embodiment, a coating layer is provided on the matrixof a plurality of nanotube bundles. Coating layer surrounds individualnanotubes of individual nanotube bundles.

According to a second aspect of embodiments disclosed herein, there isprovided a method that includes generating EUV radiation in an EUVlithography system. The EUV radiation has passed through a coating layerof a pellicle membrane. The EUV radiation that is passed through thecoating layer of the pellicle membrane is passed through a transparentlayer of the pellicle membrane. The EUV radiation that has passedthrough the transparent layer of the pellicle membrane is reflected froma mask and received at a semiconductor substrate.

According to a third aspect of embodiments disclosed herein, there isprovided a method that includes generating EUV radiation in an EUVlithography system. The EUV radiation is passed through a coating layerof a pellicle membrane. The EUV radiation that has passed through thecoating layer of the pellicle membrane is passed through a matrix ofnanotubes of the pellicle membrane. The EUV radiation that has passedthrough the matrix of nanotubes of the pellicle membrane is reflectedfrom a mask and received at a semiconductor substrate.

The various embodiments described above can be combined to providefurther embodiments. Aspects of the embodiments can be modified, ifnecessary, to employ concepts of the various patents, applications andpublications to provide yet further embodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. An optical assembly, comprising: a matrix of a plurality of nanotubesbundles; and a coating layer on the plurality of nanotube bundles, thecoating layer surrounding individual nanotubes of the individualnanotube bundles.
 2. The optical assembly of claim 1, wherein thecoating layer includes one or more of boron (B), boron silicon nitride(BNSi), silicon nitride (Si3N4), silicon dinitride (SiN2), niobium (Nb),niobium nitride (NbN), niobium monosilicide (NbSi), niobium silicide(NbSi2), niobium silicon nitride (NbSiN), niobium titanium nitride(NbTixNy), molybdenum (Mo), molybdenum nitride (MoN2), molybdenumcarbide (Mo2C and Mo4C, molybdenum silicide (MoSi2), molybdenum siliconnitride (MoSixNy), zironcium nitride (ZrN), zirconium fluoride (ZrF4),yttrium nitride (YN), yttrium fluoride (YF), titanium nitride (TiN),titanium carbon nitride (TiCxNy), hafnium nitride (HfNx), hafniumfluoride (HfF4) and vanadium nitride (VN).
 3. The optical assembly ofclaim 1, wherein the coating layer includes one or more of boron (B),boron silicon nitride (BNSi), silicon nitride (Si3N4), silicon dinitride(SiN2), niobium (Nb), niobium nitride (NbN), niobium monosilicide(NbSi), niobium silicide (NbSi2), niobium silicon nitride (NbSiN),niobium titanium nitride (NbTixNy), zironcium nitride (ZrN), zirconiumfluoride (ZrF4), yttrium nitride (YN), yttrium fluoride (YF), titaniumnitride (TiN), titanium carbon nitride (TiCxNy), hafnium nitride (HfNx),hafnium fluoride (HfF4) and vanadium nitride (VN).
 4. The opticalassembly of claim 1, further comprising a plurality of individualunbundled nanotubes.
 5. The optical assembly of claim 4, wherein acoating layer is on the plurality of individual unbundled nanotubes. 6.The optical assembly of claim 1, wherein the coating layer on theplurality of nanotube bundles includes a coating layer on a nanotubebundle and a coating layer on individual carbon nanotubes of thenanotube bundle.
 7. The optical assembly of claim 1, wherein theplurality of nanotube bundles include carbon nanotubes.
 8. A method,comprising: generating EUV radiation in an extreme ultraviolet (EUV)lithography system; passing the extreme ultraviolet radiation through acoating layer of a pellicle membrane; passing the extreme ultravioletradiation that has passed through the coating layer through atransparent layer of the pellicle membrane; reflecting the extremeultraviolet radiation that has passed through the transparent layer froma mask; and receiving the extreme ultraviolet radiation, reflected bythe mask, at a semiconductor substrate.
 9. The method of claim 8,wherein the transparent layer of the pellicle membrane includespolycrystalline silicon (poly-Si), amorphous silicon (a-Si), dopedsilicon or a doped silicon-based compound, carbon nanotube, siliconcarbon nanotube or boron nitride nanotube.
 10. The method of claim 8,wherein the transparent layer of the pellicle membrane includespolycrystalline silicon (poly-Si), silicon nitride (SixN_(y)), siliconcarbide (SiC) or molybdenum silicon nitride (MoSixNy).
 11. The method ofclaim 10, wherein the coating layer includes one or more of boron (B),boron nitride (BN), boron silicon nitride (BNSi), boron carbide (B4C),boron silicon carbide (BCSi), silicon mononitride (SiN), silicon nitride(Si3N4), silicon dinitride (SiN2), silicon carbide (SiC), silicon carbonnitride (SiCxNy), niobium (Nb), niobium nitride (NbN), niobiummonosilicide (NbSi), niobium silicide (NbSi2), niobium silicon nitride(NbSiN), niobium titanium nitride (NbTixNy), zironcium nitride (ZrN),zirconium fluoride (ZrF4), yttrium nitride (YN), yttrium fluoride (YF),molybdenum (Mo), molybdenum nitride (MoN2), molybdenum carbide (Mo2C andMo4C), ruthenium-niobium alloys (RuNb), ruthenium silicon nitride(RuSiN), titanium nitride (TiN), titanium carbon nitride (TiCxNy),hafnium nitride (HfNx), hafnium fluoride (HfF4) and vanadium nitride(VN).
 12. The method of claim 10, wherein the coating layer includes oneor more of boron (B), boron silicon nitride (BNSi), silicon nitride(Si3N4), silicon dinitride (SiN2), niobium (Nb), niobium nitride (NbN),niobium monosilicide (NbSi), niobium silicide (NbSi2), niobium siliconnitride (NbSiN), niobium titanium nitride (NbTixNy), zironcium nitride(ZrN), zirconium fluoride (ZrF4), yttrium nitride (YN), yttrium fluoride(YF), titanium nitride (TiN), titanium carbon nitride (TiCxNy), hafniumnitride (HfNx), hafnium fluoride (HfF4) and vanadium nitride (VN). 13.The method of claim 8, further comprising passing the extremeultraviolet radiation that has passed through the transparent layer ofthe pellicle membrane into a second coating layer of the pelliclemembrane.
 14. The method of claim 8, wherein passing the extremeultraviolet radiation through a coating layer of a pellicle membraneincludes passing the extreme ultraviolet radiation through a firstcoating layer and then passing the extreme ultraviolet radiation thathas passed through the first coating layer through a second coatinglayer before passing the extreme ultraviolet radiation through thetransparent layer.
 15. A method comprising: forming a matrix ofnanotubes; forming, by a first process, a protective layer on thenanotubes of the matrix of nanotubes; and forming, by a second process acoating layer over the protective layer.
 16. The method of claim 15,wherein the nanotubes of the matrix of nanotubes includes a plurality ofindividual unbundled nanotubes.
 17. The method of claim 15, wherein thenanotubes of the matrix of nanotubes includes a plurality of bundlednanotubes.
 18. The method of claim 17, wherein the bundled nanotubesinclude seven or more individual nanotubes.
 19. The method of claim 15,wherein the nanotubes are carbon nanotubes.
 20. The method of claim, 15,wherein the forming, by the first process includes forming two or moreprotective layers using two or more cycles of thermal atomic layerdeposition.